1. Field of the Invention
The invention relates to powered surgical devices. More particularly, the invention relates to rechargeable batteries used in powered surgical devices. Still more particularly, the invention relates to methods and apparatus used to sterilize and charge batteries used in powered surgical devices.
2. Description of the Prior Art
The use of rechargeable batteries in powered surgical devices used in the sterile surgical field is well known. After each use the batteries must be charged and sterilized, preferably by autoclaving. It is known that if the batteries are charged before being autoclaved they lose a significant portion of the charge and their useful life due to the heat of the sterilization process. If the batteries are charged after being autoclaved, the sterility is compromised by exposure to the battery charger. A solution to this problem has been identified in U.S. Pat. No. 4,641,076 (Linden), Method and Apparatus for Sterilizing and Charging Batteries, assigned to the assignee hereof and incorporated by reference herein.
While the invention disclosed in the aforementioned Linden patent is advantageous in that it provides a sterilization/charging container which enables a battery to be sterilized within the container and then charged within the container while in a sterile state, the invention relates to improvements which have been discovered to increase the useful life of rechargeable, sterilizable batteries.
As mentioned, it is known that batteries, when subjected to the heat of the autoclaving process, ultimately have shorter useful lives. The battery cells are generally nickel-cadmium (Ni—Cd) and as the batteries are heated in an autoclave for a long time they reach a point where the temperature in the autoclave causes the battery's temperature to increase even further. This is due to the known self-discharge rate characteristic of Ni—Cd batteries. The rate is 1% per day at room temperature and doubles for every 10 degrees above room temperature. It is clear that at autoclave temperature, generally 270-272° F. (132-133° C.), the self-discharge rate is very high. The increasing battery temperature causes the battery to self-discharge more, again increasing the battery temperature and the cycle continues until the battery temperature is even greater than the autoclave temperature. Such thermal runaway creates the high temperatures which destroy the battery cells and cause the battery to be unable to accept a full charge in subsequent uses.
This phenomenon has been addressed in some instances by using shorter autoclave cycles to avoid reaching the point of runaway battery temperature. However, some in the medical field view this as a solution which compromises the sterility of the battery. Those with this view must either accept battery powered handpieces with relatively short battery lives or must use non-battery powered devices. Given the advantages of battery powered devices it would be desirable to produce a battery system which avoids the shortcomings of prior art battery sterilization/charging systems.
In addition to increasing the useful life of rechargeable batteries, the invention relates to improvements in operating a sterilizing/charging system such as that shown in the aforementioned Linden U.S. Pat. No. 4,641,076.
Accordingly, it is an object of this invention to provide a system for storing and charging batteries for surgical powered instruments.
It is also an object of this invention to provide a system which enables one or more batteries to be retained in a sterilization/charging container in which the batteries may be sterilized and then charged while in a sterile state.
It is another object of this invention to provide a system for charging sterilized batteries while optimizing the useful life of autoclaved batteries.
It is also an object of this invention to provide a system by which the mateable engagement of a sterilization/charging container containing rechargeable batteries and a charger is facilitated.